1. Field of the Invention
The present invention relates to a light emitting device of III–V group compound semiconductor, and more particularly to improvement in efficiency of externally extracting light from a light emitting device capable of emitting blue or white light and improvement in controllability of its emission characteristics.
2. Description of the Background Art
Conventionally, a sapphire substrate has primarily been used for a light emitting device of III group compound semiconductor, and a nitride semiconductor light emitting device including such a sapphire substrate has been commercially available. Since the sapphire substrate is insulative, an electrode for a p-type semiconductor (hereinafter, referred to as “p-electrode”) and an electrode for an n-type semiconductor (hereinafter, referred to as “n-electrode”) are both arranged on a plurality of III group nitride semiconductor layers grown on a main surface of the substrate.
FIG. 10 is a schematic cross sectional view of a light emitting device of a compound semiconductor disclosed in Japanese Patent Laying-Open No. 2003-163373. This light emitting device includes a plurality of reflective layers. More specifically, in the light emitting device of FIG. 10, a buffer layer 82, a first reflective layer 86, an n-type layer 83, a light emitting layer 84, a p-type layer 85, a second reflective layer 87, and a p-electrode 88 are stacked successively on a sapphire substrate 81. An n-electrode 89 is formed on n-type layer 83 partially exposed. In the example shown in FIG. 10, second reflective layer 87 serves as p-electrode 88 as well.
In the light emitting device of FIG. 10, light emitted from light emitting layer 84 comes to resonate between first reflective layer 86 and second reflective layer 87, and is emitted efficiently to the outside via sapphire substrate 81, leading to improvement in optical output of the light emitting device. To this end, first reflective layer 86 has reflectance lower than that of second reflective layer 87.
Further, Japanese Patent Laying-Open No. 2002-026392 discloses provision of an electrode of high reflectance on the p-type layer side in a similar manner, to cause light from the light emitting layer to be reflected to the sapphire substrate side, to thereby improve the efficiency of externally extracting light.
In each of the light emitting devices disclosed in Japanese Patent Laying-Open Nos. 2003-163373 and 2002-026392, a metal layer of high reflectance is provided on the p-type GaN layer, and light from the active layer is reflected dependent on the device structure before being emitted via the substrate. As such, in the case that molding is carried out after dividing a wafer including the semiconductor layers into chips, extraction of light from the light emitting device is restricted with the emission characteristics dependent on the device structure. To change the emission characteristics, it is necessary to appropriately design the cup shape or mold shape in the molding.